IMC reporter thought aircraft in close proximity account loud sound similar to aircraft departing.

Attributes
ACN	97669
Time
Date	198811
Day	Sun
Local Time Of Day	0601 To 1200
Place
Locale Reference	airport : ord
State Reference	IL
Altitude	msl bound lower : 2500 msl bound upper : 2500
Environment
Flight Conditions	IMC
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : ord
Operator	common carrier : air carrier
Make Model Name	Large Transport, Low Wing, 3 Turbojet Eng
Flight Phase	descent : approach
Flight Plan	IFR
Aircraft 2
Operator	other
Make Model Name	Medium Large Transport, Low Wing, 2 Turbojet Eng
Flight Phase	climbout : takeoff climbout : initial
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Experience	flight time last 90 days : 200 flight time total : 15000 flight time type : 7000
ASRS Report	97669
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : flight engineer pilot : cfi pilot : atp
Experience	flight time last 90 days : 200 flight time total : 8000 flight time type : 2300
ASRS Report	97690
Events
Anomaly	other anomaly other
Independent Detector	other flight crewa
Resolutory Action	none taken : anomaly accepted
Consequence	faa : reviewed incident with flight crew
Miss Distance	horizontal : 200 vertical : 1500
Supplementary
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	other

Narrative:

We were on the localizer and G/south of runway 22R at ord, inside of saltz, and cleared for the ord runway 22R ILS approach. Our altitude was about 2500' and turbulence was moderate. We heard another jet pwred aircraft very loud, very close to us for the better part of 30 seconds. I notified ord dispatch and talked to ord TRACON after we landed. The noise was the same as we hear in our airplane cockpit when we are at the hold line. The next airplane for takeoff, and the aircraft in position, applies takeoff thrust and departs. The only difference was in our case, the loudness continued longer than when we listened to our aircraft takeoff from our cockpit. I have been a crew member on air carrier for 18 yrs out of my 22 yrs with the company. The noise we heard was definitely not from our own air conditioning system or any other source inside our aircraft. Ord TRACON indicated that no C/a's were generated by their equipment. I filed a near miss report with ord TRACON in another telephone conversation. Callback conversation with reporter revealed the following: company and union investigated the incident further and were advised a military aircraft, jet medium large transport, had departed ngu and apparently passed in the vicinity of the arriving large transport. Content at no time were the aircraft closer than 1500'.

Original NASA ASRS Text

Title: IMC REPORTER THOUGHT ACFT IN CLOSE PROX ACCOUNT LOUD SOUND SIMILAR TO ACFT DEPARTING.

Narrative: WE WERE ON THE LOC AND G/S OF RWY 22R AT ORD, INSIDE OF SALTZ, AND CLRED FOR THE ORD RWY 22R ILS APCH. OUR ALT WAS ABOUT 2500' AND TURB WAS MODERATE. WE HEARD ANOTHER JET PWRED ACFT VERY LOUD, VERY CLOSE TO US FOR THE BETTER PART OF 30 SECS. I NOTIFIED ORD DISPATCH AND TALKED TO ORD TRACON AFTER WE LANDED. THE NOISE WAS THE SAME AS WE HEAR IN OUR AIRPLANE COCKPIT WHEN WE ARE AT THE HOLD LINE. THE NEXT AIRPLANE FOR TKOF, AND THE ACFT IN POS, APPLIES TKOF THRUST AND DEPARTS. THE ONLY DIFFERENCE WAS IN OUR CASE, THE LOUDNESS CONTINUED LONGER THAN WHEN WE LISTENED TO OUR ACFT TKOF FROM OUR COCKPIT. I HAVE BEEN A CREW MEMBER ON ACR FOR 18 YRS OUT OF MY 22 YRS WITH THE COMPANY. THE NOISE WE HEARD WAS DEFINITELY NOT FROM OUR OWN AIR CONDITIONING SYS OR ANY OTHER SOURCE INSIDE OUR ACFT. ORD TRACON INDICATED THAT NO C/A'S WERE GENERATED BY THEIR EQUIP. I FILED A NEAR MISS RPT WITH ORD TRACON IN ANOTHER TELEPHONE CONVERSATION. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING: COMPANY AND UNION INVESTIGATED THE INCIDENT FURTHER AND WERE ADVISED A MIL ACFT, JET MLG, HAD DEPARTED NGU AND APPARENTLY PASSED IN THE VICINITY OF THE ARRIVING LGT. CONTENT AT NO TIME WERE THE ACFT CLOSER THAN 1500'.

Data retrieved from NASA's ASRS site as of August 2007 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.